(a) Technical Field
The present disclosure relates, generally, to a membrane humidifier for a fuel cell. More particularly, it relates to a membrane humidifier for a fuel cell, which humidifies dry air by water exchange between the dry air and humid air discharged from a fuel cell stack and suitably supplies the humidified air to the fuel cell stack.
(b) Background Art
A fuel cell is an electricity generation system that does not convert chemical energy of fuel into heat by combustion, but electrochemically converts the chemical energy directly into electrical energy in a fuel cell stack. Such a fuel cell can be suitably applied to the supply of electric power for small-sized electrical/electronic devices such as portable devices, as well as to the supply of electric power for industry, homes, and vehicles, for example.
At present, a preferred fuel cell for a vehicle is a polymer electrolyte membrane fuel cell (PEMFC), also called a proton exchange membrane fuel cell, which preferably comprises: a membrane electrode assembly (MEA) including a polymer electrolyte membrane (PEM) for transporting hydrogen ions and an electrode catalyst layer, in which an electrochemical reaction takes place, suitably disposed on both sides of the PEM; a gas diffusion layer (GDL) for uniformly diffusing reactant gases and transmitting generated electricity; a gasket and a sealing member for suitably maintaining airtightness of the reactant gases and coolant and providing an appropriate bonding pressure; and a bipolar plate for transferring the reactant gases and coolant.
Preferably, in the fuel cell having the above-described configuration, hydrogen as a preferred fuel and oxygen (air) as a preferred oxidizing agent are suitably supplied to an anode and a cathode through flow fields of the bipolar plate, respectively. Preferably, the hydrogen is suitably supplied to the anode (that can also be called a “fuel electrode”, “hydrogen electrode”, and “oxidation electrode”) and the oxygen (air) is suitably supplied to the cathode (that can also be called an “air electrode”, “oxygen electrode”, and “reduction electrode”).
Preferably, the hydrogen supplied to the anode is dissociated into hydrogen ions (protons, H+) and electrons (e−) by catalyst of the electrode catalyst layer, where the catalyst is preferably provided on both sides of the electrolyte membrane. At this time, only the hydrogen ions are selectively transmitted to the cathode through the electrolyte membrane, which is preferably a cation exchange membrane and, at the same time, the electrons are transmitted to the anode through the GDL and the bipolar plate, which are conductors.
At the cathode, the hydrogen ions supplied through the electrolyte membrane and the electrons transmitted through the bipolar plate meet the oxygen in the air supplied to the cathode by an air supplier and cause a reaction that produces water. Due to the movement of hydrogen ions occurring at this time, the flow of electrons through an external conducting wire occurs, and thus a current is suitably generated.
Further, the PEMFC requires water for its operation and, since the water serves as a suitable transport medium for hydrogen ions, the humidity of reactant gases is directly related to the performance of the fuel cell. Therefore, the air (or oxygen) supplied to the cathode of the fuel cell is suitably humidified at an air inlet of the fuel cell stack by a humidifier.
Although there are various suitable humidification methods, such as bubbler, steam injection, adsorption, etc., a membrane humidifier having a relatively small volume is widely employed in the fuel cell vehicle due to limitations in terms of packaging. Accordingly, a membrane humidifier has a considerable advantage in that it does not require any power, as well as the advantage of its packaging.
Preferably, the membrane humidifier is suitably configured such that the dry air supplied to a cathode inlet of the fuel cell stack receives heat and water from hot and humid exhaust gas (humid air) discharged from the cathode outlet of the fuel cell stack. However, presently employed membrane humidifiers have reduced efficiency, are expensive to manufacture, or result in deterioration of the fuel cell, for example. Accordingly, there is a need in the art for improved membrane humidifiers for a fuel cell.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.